The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

An optical fiber preform includes a silica-glass core portion, and a cladding portion surrounding the core portion, the cladding portion being composed of a fluorine-containing silica glass having a lower refractive index than the core portion, the core portion including a first region that does not include the central axis thereof, the first region containing a first dopant selected from sodium, potassium, and compounds thereof, and a second region that includes the central axis, the second region containing a second dopant that reduces the viscosity of the silica glass, the second dopant having a diffusion coefficient of 110.sup.12 cm.sup.2/s or more and less than the first dopant at 2,000 C. to 2,300 C., in which the entire core portion has an average first dopant concentration of 10 atomic ppm or more and 2,000 atomic ppm or less and an average second dopant concentration of 10 atomic ppm or more.

A glass includes a composition which is characterized by the following constituent phases of the glass: 20-80 mol % silicon dioxide; 0-40 mol % wollastonite; 0-30 mol % cordierite; 0-40 mol % anorthite; 0-40 mol % strontium-feldspar; 0-20 mol % celsian; 0-40 mol % hardystonite; 0-10 mol % titanite; and 0-15 mol % gittinsite. Where the composition is specified in mol % relative to oxides, the glass contains less than 11.5 mol % Al.sub.2O.sub.3 and less than 5000 ppm (molar, relative to the oxides) of each of B.sub.2O.sub.3, Li.sub.2O, Na.sub.2O, K.sub.2O, Rb.sub.2O and Cs.sub.2O. A calculated value for the removal rate according to ISO 695 is not more than 81.9 mg/(dm.sup.2 3 h) and a calculated value for the removal rate in acid according to DIN12116 is less than 3.5 mg(dm.sup.2 6 h).

The present invention discloses a glass-ceramic article and a glass-ceramic for an electric device cover plate, the glass-ceramic comprises, as a predominant crystalline phase, lithium silicate and the quartz crystalline phase, and has a composition expressed in weight percent including: SiO.sub.2: 65-85%, Al.sub.2O.sub.3: 1-15%, Li.sub.2O: 5-15%, ZrO.sub.2: 0.1-10%, P.sub.2O.sub.5: 0.1-10%, K.sub.2O: 0-10%, MgO: 0-10%, ZnO: 0-10%, and Na.sub.2O: 0-5%, wherein (SiO.sub.2+Al.sub.2O.sub.3+Li.sub.2O+ZrO.sub.2)/P.sub.2O.sub.5 is 40-90, the falling ball test height is 700 mm or more. By reasonable component design, the present invention achieves excellent mechanical properties of the glass-ceramic and the glass-ceramic article of the present invention and obtains the glass-ceramic or the glass-ceramic article suitable for electronic devices at a lower cost.

The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

The present invention discloses a glass-ceramic article and a glass-ceramic for an electric device cover plate, the glass-ceramic comprises, as a predominant crystalline phase, lithium silicate and the quartz crystalline phase, and has a composition expressed in weight percent including: SiO.sub.2: 65-85%, Al.sub.2O.sub.3: 1-15%, Li.sub.2O: 5-15%, ZrO.sub.2: 0.1-10%, P.sub.2O.sub.5: 0.1-10%, K.sub.2O: 0-10%, MgO: 0-10%, ZnO: 0-10%, and Na.sub.2O: 0-5%, wherein (SiO.sub.2+Al.sub.2O.sub.3+Li.sub.2O+ZrO.sub.2)/P.sub.2O.sub.5 is 40-90, the falling ball test height is 700 mm or more. By reasonable component design, the present invention achieves excellent mechanical properties of the glass-ceramic and the glass-ceramic article of the present invention and obtains the glass-ceramic or the glass-ceramic article suitable for electronic devices at a lower cost.

A silicate-based glass composition includes: 50-70 wt. % SiO.sub.2, 0.01-10 wt. % P.sub.2O.sub.5, 10-30 wt. % Na.sub.2O, 0.01-10 wt. % CaO, 0.01-10 wt. % MO, and 15-30 wt. % R.sub.2O, such that MO is the sum of MgO, CaO, SrO, BeO, and BaO, and R.sub.2O is the sum of Na.sub.2O, K.sub.2O, Li.sub.2O, Rb.sub.2O, and Cs.sub.2O.

Provided is an optical fiber containing an alkali metal element or the like having a smaller diffusion coefficient than K and having a low Rayleigh scattering loss. An optical fiber is composed of silica glass and includes a core and a cladding arranged to surround the core which has a lower refractive index than the core. The core includes a first core including a central axis and a second core arranged to surround the first core. The average concentration of an alkali metal element or alkaline-earth metal element in the first core is 10 mol ppm or less. The average concentration of chlorine in the first core is 2000 mol ppm or more. The average concentration of an alkali metal element or alkaline-earth metal element in the second core is 10 mol ppm or more. The average concentration of chlorine in the second core is 10 to 600 mol ppm.

A method of producing a glass briquette in which reclaimed glass fines are mixed with a binder material to create a mixture. The mixture is subsequently compressed in a chamber to form a briquette having the shape of the interior of the chamber. The reclaimed glass includes glass fines of a size of smaller than 10 mm. The method is performed without melting the glass fines such that the resulting briquette contains the discrete glass fines held in the binder and may be used as a furnace ingredient for later glass product production. The glass briquette may contain other batch ingredients required in the production of glass.

Provided is a glass composition comprising a glass frit containing P.sub.2O.sub.5, BaO, ZnO, group I-based oxide and group II-based oxide, wherein the P.sub.2O.sub.5 is contained in an amount of 20 wt % to 55 wt % based on a total weight of the glass frit, wherein each of the BaO and ZnO is contained in an amount of 2 to 30% by weight based on the total weight of the glass frit, wherein the group I-based oxide is contained in an amount of 5 to 20% by weight based on the total weight of the glass frit, wherein the group II-based oxide is contained in an amount of 1 to 15% by weight based on the total weight of the glass frit.